The present invention relates to a high performance friction material for use in automobile brakes which consists of steel wool as a major portion of the reinforcing material.
As used herein "friction particle" is intended to mean a particulate material having the properties of no substantial softening at elevated temperatures and a material which will not flow together or cohere with other particles, as would be the case with a "friction binder". A "friction particle" will not fuse with like friction particles, and is insoluble. A friction particle is held in place with a friction binder.
As used herein, a "friction binder" has the properties of flowability and adhesive and cohesive binding action, for the purpose of binding together a reinforcing material and other additives (including a friction particle) necessary for building a brake lining or other similar article of manufacture.
As used herein, a "friction material" is a composition useful as linings or facings in brakes, main clutches, and banded clutch facings of power transmission speed control structures of powerdriven devices such as automotive vehicles. Friction materials as now made are composed in general of a filamentous reinforcing material, bonded with a friction binder and containing other organic or mineral friction controlling agents such as friction particles.
Conventionally, components of friction materials consist of asbestos as a major portion of the reinforcing component and thermosetting resins, cashew-nut-shell-oil friction particles, barium sulfate, graphite etc. are incorporated therein. However, a problem has recently occurred because asbestos contains a carcinogenic substance. On the other hand, automotive makers have become more severe in requirements for this kind of friction material for reduction of friction wear. As a result, some suppliers have already begun to substitute other materials for asbestos to meet the requirements of better performance of friction material or to circumvent the regulations imposed on asbestos.
Among the reinforcements for non-asbestos friction materials, attention is called at the present time to steel wool because of its relatively low cost. However, when using steel wool for a reinforcement, the "wetting effect" of thermosetting resins, which perform as binders in the molding process, is inferior compared to asbestos. This results in a fatal drawback of lowering the strength of friction parts which is a vital physical characteristic.